envsubst command getting stuck in a container

I encountered the same issues, and after much research and fishing through the internet. I managed to find a few work arounds to this issue. Below I'll list them and identifiable risks at the time of this "Answer post"

Solutions:

1.) apt-get install -y gettext its a standard GNU package language library, one of these libraries that it includes is envsubst` and I can confirm that it works for docker UBUNTU:latest and it should work for every flavored version.

2.) npm install envsub dependent on the "use case" - this approach would be better supported by node based projects.

3.) enstub cli project lib in my opinion it seems a bit overkill to downloading a custom cli from a random stranger but, it's also another option.

Risk:

• apt-get install -y gettext:

  1.) gettext - this approach would NOT be ideal for VM's as with any package library, it requires maintenance and updates as time passes. However, this isn't necessary for docker because once an a container is initialized and up and running we can create a bashscript to add the package, substitute env vars and then remove the package.

  2.) It's a bad idea for VM's because it can be used to execute arbitrary code

• npm install ensub

  1.) envsub - updating packages and this approach wouldn't be ideal if your dealing with a different stack and not using nodejs.

NOTE: There's also a PHP version for those developing a PHP application and it seems to work PHP's cli if you need a custom environment.

Resources:

• GetText package library info: https://www.gnu.org/software/gettext/
• GetText Risk - https://ubuntu.com/security/notices/USN-3815-2
• PHP-GetText - apt-get install -y php-gettext
• Custom ensubst cli: https://github.com/a8m/envsubst

This is likely because $MYENV is not available for envsubst when you run the image.

Each RUN command runs on its own shell.

From the Docker documentations:

RUN (the command is run in a shell - /bin/sh -c - shell form)

You need to source your profile as well, for example if the $MYENV environment variable is available in the .bashrc file, you can modify your Dockerfile like this:

RUN source ~/.bashrc && envsubst < src/js/envapp.js > src/js/app.js

I had some issues with envsubst in Docker. For some reasons envsubst doesn't work when I try to copy the output in the same file. For example, this is not working:

RUN envsubst < file.conf > file.conf

But when I when I tried to use a temp file the issue disappeared:

RUN envsubst < file.conf > file.conf.temp && cp -f file.conf.temp file.conf